Mammography machines are used for X-ray examination of the female human breast (the milk-producing organ) to detect cancer or other growths. A typical machine is described in detail in U.S. Pat. No. 5,164,976, the disclosure of which is hereby incorporated by reference. FIG. 1 depicts a conventional mammography machine shown in the above United States Patent. The mammography machine includes an operator control unit and X-ray generator portion indicated at 20. The portion 20 incorporates the control electronics for the machine as well as the power supply for an X-ray source. The machine portion indicated at 22 is sometimes referred as a C-arm assembly and includes a film table 24, an overlaying compression paddle 26 and an X-ray source 28. The C-arm assembly may be rotatable about a horizontal axis 30 for obtaining different angular images. A radiation shield 32 isolates the operator control area adjacent portion 30 from the patient area adjacent film table 24. The C-arm 22 is vertically adjustable, in the position shown in FIG. 1, to accommodate date patients of different heights. The table 24 accepts standard X-ray film cassettes for image recording.
In conducting a mammography examination, a patient's breast is placed upon film table 24 and is compressed by compression paddle 26. The compression is required in order to have a substantially uniform density or thickness of the breast typically necessary to provide rather uniform X-ray image density characteristics. The reason is that the conventional X-ray films have relatively small dynamic ranges, and therefore the X-ray beam intensity must be within a certain small variation when reaching the film table 24. Otherwise, higher intensity area will be overexposed or lower intensity area will be underexposed depending on the exposure time.
The foregoing mammography machine includes many drawbacks. One of the most obvious ones is demonstrated in FIG. 2, wherein two cancer areas 80 and 82 are shown in a patient's breast 38. If the breast 38 is compressed by the compression paddle 26, the cancer area 82 moves toward the center of the field of view while the cancer area 80 moves out of the field of view. This means that there is a significant possibility that we cannot detect a cancer being located near the chest wall. Another disadvantage is that the compression procedures are often painful for patients having smaller breasts due to higher compression force.